Build events-kafka plugin on stable-3.13

Change-Id: Ice255acb26b5331c01d0c675346dccd7218673e1

jenkins/gerrit-bazel-plugin-events-kafka.yaml

diff --git a/jenkins/gerrit-bazel-plugin-events-kafka.yaml b/jenkins/gerrit-bazel-plugin-events-kafka.yaml
index 32f6ec5..1c39fcd 100644
--- a/jenkins/gerrit-bazel-plugin-events-kafka.yaml
+++ b/jenkins/gerrit-bazel-plugin-events-kafka.yaml
@@ -12,5 +12,6 @@
       - 'plugin-{name}-gh-bazel-{branch}':
           branch:
             - master
+            - stable-3.13
       - 'plugin-{name}-verifier'
       - 'plugin-{name}-verifier-gh'